A polymer battery, which is also called a lithium secondary battery, generates current by the migration of lithium ions. The polymer battery includes a polymer battery module having a polyelectrolyte and positive and negative electrodes formed of active polymers, and a protective package for containing the polymer battery module.
The polymer battery is used as a power supply for personal computers, portable terminal devices (portable telephone sets and PDAs), video cameras, electric vehicles, energy storage batteries, robots, artificial satellites and the like.
The package of the polymer battery is a cylindrical or parallelepipedic metal can formed by pressing a metal sheet or a pouch formed by processing a laminated sheet consisting of a base layer, an aluminum layer and a sealant layer.
Such known packages for polymer batteries have the following problems. The metal can has rigid walls and hence the shape of the lithium battery module is dependent on that of the metal can. Since the hardware is designed so as to conform to the shape of the battery, the dimensions of the hardware are dependent on the shape of the battery, which reduces the degree of freedom of designing the shape of the hardware.
A pouch formed by heat-sealing two laminated sheets to contain a polymer battery module therein and an embossed package formed in the shape of a vessel by subjecting the laminated sheet to an embossing process to contain a polymer battery therein have been developed. The embossed package,as compared with the pouch, is a compact package. Satisfactory moistureproof property, strength including piecing resistance and insulating property are essential to polymer battery packages.
The polymer battery module is put in a package and peripheral parts of the package is heat-sealed hermetically. The polymer battery module is provided with electrodes having the shape of a plate, i.e., tabs, to supply an electric current produced therein to an external device. Therefore, the tabs are sandwiched between the walls of the package when sealing the package by heat-sealing. Since the tabs have a thickness in the range of 50 to 200 μm, it is possible that a resin forming the heat-sealable layer of the package is unable to fill up unsealed gaps formed beside the opposite sides of the tabs and the package cannot be sealed perfectly.